Means for increasing the brightness of a cathode tube display



N. sTRAEHL MEANS FOR INCREASING THE. BRIGHTNESS `Fuly 2l, 1953 OF AvCTHODE TUBE DISPLAY` 2 Sheng-Sheet 1.

Filed Aug. 3, 1950 Ill" ROBERT N. STRAEHL ATTORNEY.

July 21, l953 R. N. STRAEHU j MEANS FOR INCREASING THEVRIGHTNSS oF Acm1-pps TUBE DISPLAY Y' 2 Sheets-Sheet 2 Filed Aug. 3, 1950 l JNVENTOR.ROBERT N. STRAEHL ATTORNEY.

Patented July 21,l 1953 MEANS FOR INCREASING THE BRIGHTNESS F A CATHODETUBE DISPLAY Robert N. Straehl, Danbury, Conn., assgnor to SperryProducts, Inc., Danbury, Conn., a cor' poration of New York ApplicationAugust 3, 1950, Serial No. 177,357

1 Claim.

This invention relates to ultrasonic instruments employing a cathode raytube, and has for its principal object the provision of a method andmeans for increasing the brightness of the cathode tube display. Moreparticularly, the invention relates to the type of ultrasonic testing orinspection instrument in which pulses are periodically transmitted intoobjects such as metal blocks and the time interval which elapses betweenthe transmission of the pulse and the reception of the first reflectionof the pulse is indicated on the cathode tube sweep. The sweep isnecessarily of short duration because of the small time intervals whichare to be measured, and the repetition rate of transmission of the pulse(and, hence, of the sweep which is synchronized with the pulse) must bekept low to allow sucient time for unwanted reflections from distantpoints to die out. The short time sweep and low repetition rate yield acathode tube display of less than the desired brightness.

It is therefore the principal object of this invention to provide amethod and means for increasing the brightness of the cathode ray tubedisplay under the above stated operating conditions, i. e., of fastsweep and low repetition rate.

Further objects and advantages will become apparent in the followingdetailed description thereof.

In the accompanying drawings,

Fig. 1 is an electrical block diagram embodying my invention.

Fig. 2 is a series of graphs illustrating the theory of the invention. p

Referring to Fig. 2 there is disclosed the theory of this inventionwhich, for purposes of illustration, is shown as applied to anultrasonic system in which a pulse P is repeated at a rate of 60 persecond, in other words, a pulse is propagated approximately every 16,000microseconds. The useful reections R, R. of the pulse may occur withinthe first 100 microseconds, and it is necessary to render the receiverunresponsive to further signals such as S1, S2, S3, because these arebeyond the range in which we are interested. Ordinarily, therefore,there would be a period of 15,9001 microseconds of inactivity of thecathode ray indicator until the next repetition of the pulse. By thisinvention I utilize this dead or inactive interval to obtain amultiplicity of repetitions of the desired indications R, R on thecathode ray screen, thus greatly multiplying and intensifying thedesired indications.

'Ihe means whereby I accomplish the above result is disclosed in Fig. 1wherein a trigger or repetition rate generator l0 energized from asuitable source such as cycle A. C. actuates a pulse generator ortransmitter 60 times per second. The pulse is applied to a quartzcrystal l2 which transforms the electrical Vibrations into mechanicalvibrations which are transmitted into a work-piece l5 which is to beinspected. The pulse enters through surface I6 and will be reflectedfrom any reflecting surface therein such as defect Il. Both thetransmitted pulse and reflections thereof are received by a receiver 20whose output is applied (through intermediate devices to be describedhereinafter) to the vertical plates 2| of a cathode ray oscilloscope 22to deflect a horizontal sweep between horizontal plates 23. The sweep isgenerated by a sweep generator 25 synchronizedk with the pulse.

As stated in the introduction hereto, the echoes occurring in arelatively small time interval, for example, microseconds correspondingto travel of the pulse through l ft. of aluminum, may be of interest,Whereas indications received thereafter and until the next repetition ofthe pulse are of no interest to the operator. In the example chosen, thetime interval which does not contain desired information is on the orderof 15,900 microseconds. In order to limit reception to the desired timeinterval (in the example given, 100 microseconds) there is Yenergized acoincidence gate circuit 30 of the type which is effective only when twoinputsare applied, the gate 36 being energized by the output of receiver20 in response to the generated pulse P and by a gating pulse 100microseconds wide generated by a short gate generator which may be amultivibrator 3| energized from the repetition rate generator I0. Thus,upon each generation of pulse P, gate 30 will pass output from receiver2i] for the desired time interval (in this case, 100 microseconds) Ifthe pulse repetition rate is 60 times per second, there will be arelatively long interval (in this case, 15,900 microseconds) before thenext pulse is transmitted. I utilize this time interval to securerepetition of the desired indications on the cathode ray tube. For thispurpose, the repetition rate generator renders -effcctive a long gategenerator 4I at the same time that short rate generator 3| is renderedeffective. In the example chosen, if the gating pulse generated by gate3| is 100 microseconds wide, the gating pulse generated by gate 4| willbe just short of 16,000 microseconds, such as, for example, 15,900microseconds. The pulse generated by gate di permits operation of thefree-running sweep generator 25 which can thus be set to repeat thesweep each 100 microsec# ends (see Fig. 2e). At the same time, vthegen-,leraticn of theilong gate is applied to coincidence gate circuit :iwhose other source of energiza tion is a memory circuit energized romtheoutput of short-period.. gate 30.l Thus, once gate circuit 30 allowssignals to pass for the desired short period (in this example, 100microseconds), futher reception of signals is cut oli (see Fig. 2a). Thesignal output from gate 30 will, however, be

repeated by the memory circuit which includesr long-period gate lil)(see Fig. 2c) as long as said gate is effective (in this example, for15,900 microseconds). In other words, instead of signal voltages R, Rbeing indicated once every 16,000 microseconds on the cathode ray tube,these indications will appear 159 times in the same time intervalbetween pulses (see Fig. 2d)

The memory loop may comprise any suitable acoustic delay line 50 to oneend of which the output of receiver 2li may be applied for the intervalthat gate 30 is effective, and the other end of which is connected to anamplier 5i whose output is applied to the vertical plates 2i of 1thecathode ray tube and to gate d0 which will return it to the input of thedelay line. Thus, for as long as gate 40 is effective (in this example,15,900 microseconds), the signal voltages passed by the short periodgate 30 will be circulated through the memory loop, the output at eachcircuit being applied to the vertical plates of the cathode ray tube. Aportion of the voltage output from amplier 5l may be diverted to sweepgenerator 25 by lead 55 to synchronize the sweep with output ofamplifier 5l and thus insure coincidence of the repetitions of R, R onthe sweep.

The usual acoustic delay line is a tube filled with mercury, a block ofmagnesium or other known materials having piezo-electric elements ateach end.

Having described my invention, what claim and desire to secure byLetters Patent is:

In a device of the type described, means for 4 transmitting successiveultrasonic puls-s to an object at relatively long timelitek'rvalsbetween pulses, means for receiving rei'ctibns of eachtransmittedmpuls,,means vfor rendering the receiving means ineffective arelatively short time interval after the transmission of each pulse, a

vmemory loop circuit including a time delay mechanism for introducing adelay at least equal to the length of time that said receiving means iseffective, means for discharging the output of said receiver into thememory circuit whereby said output will be repeated as long as said loopcircuit is effective, and means for indicating the signal voltagespassing through said circuit, said last-named means comprising a cathoderay tube having vertical and horizontal plates, a free-running sweepcircuit for establishing a sweep betweenthe horizontal plates, means forrendering` the sweep circuit effective in synchronism with. thetransmission of each pulse, means for synchronizing the sweep with thesignal voltages: passing through said memory circuit, the voltages-E insaid memory circuit being lapplied to the verti-I cal plates, and meansfor rendering the memory' circuit ineffective after a predetermined timein terval and before the transmission of the suc-I ceeding pulse.

ROBERT N. STRAEHL..

References Cited in the file of this patent;

UNITED STATES PATENTS Number Nam-e Date 2,370,134 Begun Feb. 2'7, 19452,378,383 Arndt June 19, 1945iy 2,378,388 Begun June 19, 1945l 2,415,119Wellenstein Feb. 4, 1947,'

OTHER REFERENCES An article'entitled Mercury Delay Line Memory Using aPulse Rate of Several Megacycles in the August 1949 issue oftheProceedings of thee I. R. EL, copy in Division 23, 235-61.

